U.S. Rep. Steve Stockman, R-Friendswood, who filed to run against U.S. Sen. John Cornyn on Dec. 9, 2013.

U.S. Rep. Steve Stockman, R-Friendswood, has filed to run against U.S. Sen. John Cornyn in the March GOP primary, joining at least eight other hopefuls vying for the senior senator's seat, according to a spokesman with the Republican Party of Texas.

Stockman, who had filed for re-election in Congressional District 36, had to withdraw from that race to seek Cornyn's seat.

In an interview with the website WND, Stockman said he was running because he was "extremely disappointed in the way [Cornyn] treated his fellow congressmen and broke the 11th commandment and undermined Ted Cruz’s fight to stop Obamacare.”

Brendan Steinhauser, Cornyn's campaign manager, released a statement saying the senior senator was "endorsed by Texas Right to Life and ranked as the 2nd most conservative senator in America."

"Sen. Cornyn looks forward to discussing his conservative record with Texans,” Steinhauser added.

As of Sept. 30, Cornyn had nearly $7 million in cash on hand, and will be a formidable incumbent. But some members of his own party have been gunning for him on the right, questioning his decision in late September not to not back U.S. Sen. Ted Cruz's tactics in opposing the Affordable Care Act. In a break with tradition, Cruz has pointedly declined to endorse Cornyn's re-election bid.

GOP political consultant Matt Mackowiak said Stockman faces an uphill battle, from recent investigations into his political and fundraising operation to Cornyn’s “huge bankroll.”

“Now we will find out if Sen. Cornyn is truly vulnerable, which I have doubted,” Mackowiak said, adding, "I predict that not one member of the congressional delegation will support Stockman. Ultimately, he will need outside groups to spend, and that is the most important unknown right now.”

Gov. Rick Perry, who was at Cornyn's side when he kicked off his re-election bid, isn't wavering one iota.

"The Governor has been very clear in his support for Senator Cornyn and nothing has changed," said Perry spokesman Rich Parsons.

Stockman, who returned to office in 2012 after a 16-year absence, recently came under fire after a Houston Chronicle investigation revealed that he violated federal ethics laws by failing to disclose a series of business affiliations, while providing no details about the business he said was his only source of income.

During his most recent stint in the House, Stockman, a member of the Science, Space and Technology and Foreign Affairs committees, has also drawn plenty of other headlines — particularly on the issue of guns.

Cornyn's other challengers in the Republican primary are relative unknowns. They include attorney and activist Linda Vega, Liberty businessman Dwayne Stovall, and Tea Party candidates Reid Reasor and Chris Mapp.

In the Democratic primary, Dallas dental mogul David Alameel faces El Paso lawyer Maxey Scherr and former GOP House candidate Michael Fjetland of Houston, who switched parties after the 2006 elections.

Stockman's entry into the Senate race leaves an open door for last-minute filers in CD-36. John Amdur of Houston and Phil Fitzgerald of Hull have filed for that race.

Texas Tribune donors or members may be quoted or mentioned in our stories, or may be the subject of them. For a complete list of contributors, click here.

Quality journalism doesn't come free

Perhaps it goes without saying — but producing quality journalism isn't cheap. At a time when newsroom resources and revenue across the country are declining, The Texas Tribune remains committed to sustaining our mission: creating a more engaged and informed Texas with every story we cover, every event we convene and every newsletter we send. As a nonprofit newsroom, we rely on members to help keep our stories free and our events open to the public. Do you value our journalism? Show us with your support.